1. Field of the Invention
The present invention relates to a surface processing apparatus, more particularly relates to a surface processing apparatus for processing a substrate surface using plasma. This surface processing apparatus is used for the fabrication of integrated circuits in the semiconductor industry. The surface processing apparatus has a plasma source for supplying ions, electrons, neutral radicals, etc. useful for formation of an insulating film, interconnect metal, gate electrode materials, etc. on a substrate or minutely processing the substrate surface. This plasma source creates plasma inside a reactor. The distribution of this plasma is controlled by a point-cusp magnetic field.
2. Description of the Related Art
The configuration of a representative surface processing apparatus of the related art will be explained first with reference to FIG. 18. FIG. 18 is a schematic view of a surface processing apparatus. This surface processing apparatus is provided with a reactor (vacuum tank or processing chamber) made of metal plate and evacuated by an attached vacuum pump 11 to a predetermined vacuum state. The reactor 12 is provided inside it with, for example, in the form of a parallel plate type electrode structure, an electrode (cathode) 13 positioned at the top and an electrode (substrate electrode) 15 positioned at the bottom and supporting the substrate (or wafer) 14. Illustration of the support structure of the electrode 15 is omitted. The substrate 14 loaded on the substrate electrode 15 is carried into through a substrate entry port 16 by a transport device (not shown). After performing predetermined processing on the substrate 14 placed on the substrate electrode 15, the substrate 14 is carried out through a substrate exit port 17. When processing the substrate 14 in the reactor 12, the inside space of the reactor 12 is evacuated to a required vacuum state, a process gas is introduced, the power feed conditions are met and plasma is generated in the front space of the substrate 14, and the substrate surface is processed by the plasma. Illustration of the mechanism for introduction of the process gas is omitted.
Looking at the configuration of the reactor 12 of the surface processing apparatus, further, the reactor 12 is held at the ground potential 18. In attachment, the cathode 13 and the substrate electrode 15 are electrically insulated from the reactor 12. In the illustrated example, the detailed structure for the insulation is omitted. Further, high frequency power sources 19 and 20 are connected independently to the cathode 13 and substrate electrode 15. These electrodes are independently supplied with high frequency power. The frequency and amount of the high frequency power are freely set in accordance with the objective.
Further, the substrate 14 arranged on the substrate electrode 15 is held by an electrostatic chucking mechanism 15a or the like. In this way, the substrate electrode 15 has the structure of a substrate holder. A predetermined amount of argon or another process gas for the surface processing or treatment of the substrate 14 is introduced into the reactor 12 and the inner pressure of the reactor 12 is maintained at a vacuum of about 1 to 10 Pa.
The back surface of the cathode 13 has a magnet plate 22 provided with a large number of magnets (permanent or coil magnets) 21. The magnet plate 22 is comprised of a plate member 22a made of a nonmagnetic member, on which a large number of rod-shaped or block-shaped magnets 21 are affixed. The rod-shaped magnets 21 all have the same length and same magnetic strength. Opposing magnetic poles (N poles and S poles) are formed on the two end faces of each magnets 21, with one end face fixed to the plate member 22a. In the magnet plate 22, the large number of magnets 21 are fixed to the surface of the plate member 22a so that their longitudinal directions are perpendicular to the surface. In the magnet plate 22, the magnetic pole end faces of the large number of magnets 18 facing the surface of the plate member 22a are arranged so as to differ among the nearest adjoining magnets. As shown in FIG. 18, N poles and S poles are arranged alternately at equal distances on the surface of the plate member 22a. Note that the magnet plate 22 may be arranged in the reactor 12 by placing the plate member 22a at the cathode 13 side or conversely placing the magnets 21 at the cathode 13 side.
As a prior art reference disclosing a structure relating to the arrangement of the large number of magnets, Japanese Unexamined Patent Publication (Kokai) No. 11-283926 (see FIG. 1, FIG. 3, FIG. 4, etc.) previously filed by the same assignee may be mentioned. Further, as other references, Japanese Unexamined Patent Publication (Kokai) Nos. 2000-144411, 6-69163, 6-316779, 8-288096, etc. may be mentioned.
In the reactor 12 of the surface processing apparatus, the surface of the substrate 13 placed on the substrate electrode 15 is processed or treated by the plasma generated at the front space 23 of the substrate 14, that is, the lower-side space of the cathode 13. This plasma is generated, for example, by electrostatic coupling of high frequency power.
FIG. 19 is a plan view of the magnet plate 22. FIG. 19 shows the arrangement of the large number of magnets 21 provided on the magnet plate 22 by a plan view. In FIG. 19, the large number of small diameter circles 21a show the end face positions and polarities of the magnetic poles of the cylindrical rod-shaped magnets 21. The plan shape of the magnet plate 22 is a circular one of substantially the same diameter as the plan shape of the substrate 14 or cathode 13. In the circular magnet plate 22, the large number of magnets 21 are arranged so as to be positioned at the four apexes of squares. This arrangement deems the positions of arrangement of the magnets to be lattice points of squares and is therefore called a “square lattice structure”. According to this square lattice structure, the periodicity of the square lattice array is maintained in the center region of the magnet plate 22, but at the peripheral edge region, the periodicity is disturbed due to the circular contour. In the example shown in FIG. 19, for example, regions 24 where magnets 21 of the same polarity (N pole) and magnets 21 of the opposite polarity (S pole) are arranged in single lines are formed at four locations. Any two nearest adjoining magnets 21 (except at diagonal positions) are in an equal distance positional relationship. In FIG. 19, the hatched circles 21a mean end faces of N poles of the magnets 21, while the remaining simple circles 21a mean end faces of S poles the magnets 21. The polarity of each of the large number of magnets 21 arranged at any square lattice point is opposite to the polarities of the other adjoining magnets 21 arranged at the nearest lattice points. In FIG. 19, the length of one side forming the square is for example 2 cm, while the diameter of the circular end face 21a of each magnet 21 is for example 8 mm.
At the inner space of the cathode 13 in the reactor 12, a cusp magnetic field is formed based on the above arrangement of the large number of magnets 21 on the magnet plate 22 arranged at the back surface of the cathode 13. This cusp magnetic field is a point-cusp magnetic field formed by the formation of magnetic field lines from the N pole toward the surrounding S poles. The large number of magnets 22 are arranged in periodic square lattice shapes in the same plane by the same magnetic force (coercive force), so the point-cusp magnetic field is also formed by a periodic distribution.
In the above surface processing apparatus, above the cathode 13 having the circular planar shape, the large number of magnets 21 are arranged in a square lattice structure due to the magnet plate 22 while being restricted by the circular attachment surface of the plate member 22a. According to this magnet array, at the inside region of the cathode 13 in the reactor 12 corresponding to the region in which the square lattice structure is maintained with accurate periodicity, the above point-cusp magnetic field is periodically repeated by the same distribution of strength. On the other hand, at the peripheral edge of the cathode 13, the periodicity of the magnet array is disturbed due to the restrictions due to the circular contour and the magnetic field lines have nowhere to go, so the magnetic field strength caused in the corresponding inside region changes and the distribution in the radial direction seen from the center of the substrate 13 becomes greatly different. In general, at the inside region of the cathode 13 in the reactor 12, the plasma density is made uniform over a broad range by causing the plasma generated in the strong magnetic field present in the region near the magnet plate 22 to diffuse in the weak magnetic field away from the magnet plate 22. According to the configuration of the conventional surface processing apparatus, however, as explained above, the weak magnetic field becomes non-uniform at the space away from the magnet plate 22 and the distribution of the magnetic field is disturbed at the peripheral edge so the density and diffusion direction of the ions and electrons in the plasma are not uniform. Therefore, the problem arises that the surface processing of the substrate 14 by the plasma becomes non-uniform.
Explaining the problem in more detail, according to the magnet plate 22 having an arrangement of magnets 21 of a square lattice structure, a strong line cusp appears at the diagonal direction 25 of the unit square lattices in a space for example at least 10 mm from the magnet plate at the peripheral edge of the magnet plate 22. As a result, there was the problem that the results of the surface processing of the substrate region corresponding to that space differed from the results of surface processing of the substrate region corresponding to another space.